As optical materials such as those for liquid crystal display devices, materials which have a low birefringence, a small coefficient of photoelasticity, and a high optical transparency are used. In the case of materials for liquid crystal display devices and the like, any materials used therein are required to have a high heat-resistance from the perspective of the manufacturing process. Glass and the like have conventionally been used as materials satisfying such requirements.
Optical materials such as those for liquid crystal display devices are generally used in the form of thin films or thin tubes or rods. Recent market requirements have called for the use of even thinner films and thinner tubes or rods. However, since the conventionally-used glass is brittle in terms of strength, it can only be used for a limited scope of use.
One example of materials having toughness is polymer materials. However, in the case of a thermoplastic resin, for example, introducing an aromatic skeleton into its molecule for allowing a high heat-resistance to be exhibited generally results in a high birefringence and a large coefficient of photoelasticity, thus making the reconciliation of high heat-resistance and optical characteristics difficult. As for thermosetting resins, conventionally known thermosetting resins are generally colored and therefore not suitable for optical material applications. Furthermore, thermosetting resins are generally polarized, which is disadvantageous for the exhibition of optical performance.
(Cases Where a Curable Composition is Used as a Transparent Conductive Film)
Transparent conductive films are plastic films which are transparent and conductive, and are functional films which are utilized in technological fields where light and electricity are involved. With recent advancements in electronics, reduction in weight, size, cost of parts and devices for which transparent conductive films are employed are desired, along with increased design flexibility and higher performance. For both conventional applications and new applications, transparent conductive films are expected to have improved functions.
Transparent conductive films are required to have a high light transmittance. In applications such as liquid crystal display and optical recording, optical characteristics such as birefringence are also regarded as important. As conventional transparent conductive films, those based on a substrate of polyester (hereinafter abbreviated as “PET”) films or polycarbonate (hereinafter abbreviated as “PC”) films, with a thin metal film or a thin semiconductor film such as ITO formed on the surface thereof, are known.
A transparent conductive film whose substrate is a PET film has a large optical anisotropy because the PET film has a molecular orientation due to a stretching operation performed during the manufacture thereof, thereby being inferior in birefringence. A transparent conductive film whose substrate is a PC film exhibits a large polarization anisotropy because the PC includes a group having a substantial polarization rate, e.g., a benzene ring, within its molecule, and therefore is likely to have birefringence.
Thus, conventional transparent conductive films have their advantages and disadvantages, and cannot necessarily be considered as satisfying the higher-level and more-complicated requirements of the recent years.
(Cases Where a Curable Composition is Used as a Component Material for a Liquid Crystal Display Device)
In recent years, liquid crystal display devices have faced some sophisticated requirements, e.g., they are required to be in a thinner film configuration, lighter in weight, larger in size, shaped arbitrarily, and capable of displaying on a curved surface. In particular, in answer to the expanded use of devices which are carried on one's body, e.g., mobile phones, electronic organizers, and pen input devices, liquid crystal display panels employing plastic substrates, as opposed to conventionally-employed glass substrates, have been contemplated and partly begun to be put to practical use. For example, polyethersulfone (hereinafter abbreviated as “PES”) and polycarbonate (PC) film substrates, which do not exhibit optical anisotropy, are available.
Plastic film substrates need to satisfy requirements such as capability to lose optical anisotropy, heat-resistance, solvent-resistance, gas barrier property, surface flatness, geometrical stability, and translucency. The aforementioned PES exhibits an increased substrate retardation when formed with a thickness of 0.1 mm or above. An increased substrate retardation leads to an increased retardation of the entire liquid crystal display device, a coloration phenomenon, and the like, thus unfavorably affecting the display quality of the liquid crystal display device. Since PES has a heat-resistance of up to 150° C., the component materials of a liquid crystal display device must be subjected to low-temperature sintering. The aforementioned PC also exhibits an increased substrate retardation when formed with a thickness of 0.1 mm or above, resulting in problems similar to those associated with PES.